bin/57903: umount: Add -d option to umount to detach vnode device

[rbranco%suse.de@localhost]

>Number:         57903
>Category:       bin
>Synopsis:       umount: Add -d option to umount to detach vnode device
>Confidential:   no
>Severity:       non-critical
>Priority:       low
>Responsible:    bin-bug-people
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Sat Feb 03 21:45:00 +0000 2024
>Originator:     Ricardo Branco
>Release:        NetBSD 10.0_RC3
>Organization:
>Environment:
>Description:
Add a -d option to umount(8) to detach a vnode device. A similar option exists in Linux's umount(8) and also FreeBSD.
>How-To-Repeat:

>Fix:
Fix: https://github.com/NetBSD/src/pull/31